The present invention relates to a transmission mechanism for a bicycle and relates more particularly to a gear transmission mechanism for driving a bicycle to move.
Conventionally, a bicycle is generally consisted of a tubular metal frame mounted on two large wire-spoked wheels, one behind the other, and equipped with handle bars and a saddlelike seat which is propelled by foot pedals through the operation of a chain transmission mechanism. This conventional chain-transmission operated structure of bicycle is not satisfactory in use because of the following disadvantages:
1. Because the chain is constantly exposed to the air it may gather rust easily causing sticking problem;
2. The chain may disconnect from the chain wheel or the rear sprocket wheel easily causing transmission failure; and
3. It is difficult to lubricate the parts of the chain transmission mechanism or to detach them for repair if a chain guard is used.